The present invention relates generally to the field of marine electromagnetic geophysical surveying. More particularly, in one or more embodiments, this invention relates to an electrode assembly for marine electromagnetic geophysical survey sources and associated methods of use, the electrode assembly comprising a carrier body and electrically conducting surfaces longitudinally spaced along the carrier body.
Marine electromagnetic geophysical surveying is used, among other purposes, to infer spatial distribution of electrical conductivity of rock formations below the bottom of a body of water, such as a lake or ocean. The spatial distribution of conductivity is used to assist in determining the presence of hydrocarbon-bearing rock formations in the subsurface, potentially resulting in cost saving by better targeted drilling operations. One type of such surveying is known as “controlled source” electromagnetic surveying (“CSEM”), which generally includes inducing a time-varying electromagnetic field in the subsurface formations and measuring one or more parameters related to a response of the subsurface rock formations to the induced electromagnetic field.
Devices for inducing such electromagnetic fields are generally termed to as electromagnetic “sources” or “transmitters” and include, among other devices, spaced apart electrodes or wire coils disposed along or at the end of a cable. The cable is typically towed by a vessel in the body of water. Time-varying electric current is imparted across the electrodes to induce a time-varying electric field in the water and subsequently in the subsurface rock formations. In some instances, the electrodes may be large, inflexible structures, such as metal cylinders or tubes. Such cylinders or tubes may be suspended at a selected depth in the water by the use of flotation devices, such as buoys. Drawbacks to these types of electrodes include difficulties in handling as these, larger, inflexible structures can be difficult to deploy and may exert undesirable stress on the cables, connectors, and flotation devices. Further drawbacks to these types of electrodes include the high power requirements that may be needed to generate the high levels of current that may be imparted across the electrodes, in some instances.